This invention concerns a three-dimensional measuring device and relates, in particular, to a measuring head capable of being fastened on a measuring machine and designed to receive at least one measuring sensor. Such devices are intended to be used with measuring machines of every precision category and possibly machine tools.
In general, these devices make it possible to follow continuously the surface of a piece to be measured, and they deliver analog measuring signals representing the position of the point of the surface scanned by the end of a sensor
One such device is described, for example, in German Utility Model No. 72 31 877. It comprises at least one measuring sensor suspended by means of a suspension device so as to be able to move in three directions at right angles to a frame. The suspension device contains for each direction of displacement, two moving bridges parallel to each other and joined by two rigid connecting elements hinged on the bridges so as to form a deformable parallelogram with them and a measuring detector provided to measure the relative displacement of the two bridges. However, in that device, the different moving bridges are placed in series under each other, which increases the overall dimensions of the assembly. Furthermore, the different displacement detectors associated with each direction are grouped at the top of the device, which necessitates complex transmission means for transmitting the motion of the different moving bridges to the displacement detectors.
Another measuring device of the type is that of the invention as described in French Patent Application No. 2,311,275. That device is more compact than the preceding one, since it is made up of moving bridges joined in pairs by elastic strips and imbricated in each other to form a parallelepiped. However, there again, the different displacement detectors are grouped at the top of the device, the elastic strips forming the sides of each deformable parallelogram not permitting those detectors to serve as support, nor as support for other useful devices such as, devices blocking certain directions of displacement of the sensor or devices limiting the oscillation of the sensor. Another disadvantage of this device associated with the use of elastic strips connecting the moving bridges in pairs parallel to each other is that the torsional strength of the different parallelograms as well as the return force they exert on the sensor are directly linked to the dimensions and mechanical characteristics of the elastic strips used and cannot then be arbitrarily defined.
That is why an object of this invention is to provide a compact three-dimensional measuring device in which the different deformable parallelograms used are imbricated in each other, but with connecting elements between the moving bridges parallel to each other which are absolutely rigid and articulated to said bridges by any rotary joint and in which the return forces of the device in a reference position are no longer defined by the elasticity of the joints.